org.openjdk.jmh.samples.JMHSample_06_FixtureLevel Maven / Gradle / Ivy

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package org.openjdk.jmh.samples;

import org.openjdk.jmh.annotations.*;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.RunnerException;
import org.openjdk.jmh.runner.options.Options;
import org.openjdk.jmh.runner.options.OptionsBuilder;

@State(Scope.Thread)
public class JMHSample_06_FixtureLevel {

    double x;

    /*
     * Fixture methods have different levels to control when they should be run.
     * There are at least three Levels available to the user. These are, from
     * top to bottom:
     *
     * Level.Trial: before or after the entire benchmark run (the sequence of iterations)
     * Level.Iteration: before or after the benchmark iteration (the sequence of invocations)
     * Level.Invocation; before or after the benchmark method invocation (WARNING: read the Javadoc before using)
     *
     * Time spent in fixture methods does not count into the performance
     * metrics, so you can use this to do some heavy-lifting.
     */

    @TearDown(Level.Iteration)
    public void check() {
        assert x > Math.PI : "Nothing changed?";
    }

    @Benchmark
    public void measureRight() {
        x++;
    }

    @Benchmark
    public void measureWrong() {
        double x = 0;
        x++;
    }

    /*
     * ============================== HOW TO RUN THIS TEST: ====================================
     *
     * You can see measureRight() yields the result, and measureWrong() fires
     * the assert at the end of first iteration! This will not generate the results
     * for measureWrong(). You can also prevent JMH for proceeding further by
     * requiring "fail on error".
     *
     * You can run this test:
     *
     * a) Via the command line:
     *    $ mvn clean install
     *    $ java -ea -jar target/benchmarks.jar JMHSample_06 -f 1
     *    (we requested single fork; there are also other options, see -h)
     *
     *    You can optionally supply -foe to fail the complete run.
     *
     * b) Via the Java API:
     *    (see the JMH homepage for possible caveats when running from IDE:
     *      http://openjdk.java.net/projects/code-tools/jmh/)
     */

    public static void main(String[] args) throws RunnerException {
        Options opt = new OptionsBuilder()
                .include(JMHSample_06_FixtureLevel.class.getSimpleName())
                .forks(1)
                .jvmArgs("-ea")
                .shouldFailOnError(false) // switch to "true" to fail the complete run
                .build();

        new Runner(opt).run();
    }

}